1. Technical Field
The present invention relates to a magenta ink composition (including both a dark magenta ink composition and a light magenta ink composition) suitable for an inkjet recording method that has not only excellent print quality and stable ejection reliability wherein foaming is suppressed, but also makes it possible to obtain inkjet recorded product with excellent resistance to moisture, ozone, and light; an ink set and ink cartridge using the aforementioned magenta ink composition; and an inkjet recording method and recorded product utilizing the same.
2. Related Art
The inkjet recording method is a publicly known method wherein droplets of an ink composition are ejected from a fine nozzle, deposited on the surface of a recording medium, and letters and images are recorded thereby. Inkjet recording methods that have reached practical application include (i) a method wherein an electric signal is converted to a mechanical signal using a piezoelectric element, an ink composition stored in the nozzle head member is ejected intermittently therefrom in accordance with the mechanical signal, the ink composition is deposited on the surface of a recording medium, and letters and images are recorded thereby, and (ii) a method wherein a part very close to the ejection member of the nozzle head is rapidly heated, a bubble is generated in the ink composition stored in the nozzle head member, the ink composition is ejected intermittently therefrom due to the expansion in volume of the bubble, the ink composition is deposited on the surface of the recording medium, and letters and images are recorded thereby.
Recently a plurality of color ink compositions have been prepared, and color images using inkjet recording have been formed thereby. Generally speaking, the forming of a color image is accomplished with three colors involving a yellow ink composition, magenta ink composition, and cyan ink composition, and in some cases with four colors wherein a black ink composition is added thereto. Additionally, color images are sometimes formed with six colors wherein a light cyan ink composition and a light magenta ink composition are added to the aforementioned four colors, or even with seven colors wherein a dark yellow ink composition is added thereto. Such a combination of two or more ink compositions is called an ink set, and normally an ink set is used in the form of an ink cartridge containing the same that is installed in a printer.
It is desirable that the ink compositions used in the inkjet recording method are generally liquids wherein various dyes are dissolved in water, an organic solvent, or a liquid mixture thereof, and the ink compositions used in forming such color images not only have excellent color themselves, but exhibit excellent intermediate color when combined with a plurality of ink compositions, and do not discolor over time when matter printed thereby is stored.
Due to continuous improvements in printing heads, ink compositions, recording methods and recording media the printing of photographic images by color inkjet printers has recently become comparable to that of silver salt photography, and the image quality thereof is on the same level as that of a photograph. On the other hand, improvements in the storage properties of images obtained thereby have been sought through refinements in ink compositions and media. Resistance to light in particular has been improved to a level whereby it presents no practical problem (see JP-A-2000-290559, JP-A-2001-288392). Still, resistance to light has not reached the same level as that of silver salt photography. The standard for evaluating light resistance capability has been to make a judgment using the discoloration rate of a pattern of pure colors (optical density near 1.0) consisting of Y (yellow), M (magenta) and C (cyan). When the light resistance capabilities of ink compositions used in printers that are currently on the market are evaluated using the above criteria, the magenta ink compositions score lowest and in many cases are the rate-limiting factor of the light resistance life of an ink set. As a result, improvement of the light resistance properties of a magenta ink composition will be effective in enhancing the light resistance of photographic images and prolonging the light resistance life of the ink set.
However, because printed matter prepared using the aforementioned ink compositions are placed not only indoors, but also outdoors, they are exposed to a variety of light sources including sunlight and to the atmosphere (ozone, NOx, SOx, etc.), and therefore ink compositions with excellent light resistance and gas resistance are being developed. The properties of light resistance and gas resistance are largely determined by the colorant used in the ink, and the development of a magenta ink composition with excellent moisture resistance in addition to these properties is needed.
Among the above properties, the compound of JP-A-2002-371079 (azo dye) and the compound of JP-A-2002-332419 (anthrapyridone dye) have been proposed as colorants with excellent light resistance and gas resistance. A magenta ink composition with excellent light resistance and gas resistance comprising a combination of two colorants has also been proposed (JP-A-2005-105136).
It has become possible to obtain an image without graininess using an ink set comprising the above light magenta ink composition by providing therewith two types of magenta ink compositions having different color densities. With these kinds of ink sets comprising two types of ink compositions having different color densities, the primary purpose thereof being the printing of photographic images, ink compositions with low color densities are generally used in the formation of photographic images to diminish or eliminate graininess. Furthermore, in the evaluation of light resistance noted above, a pattern with an optical density near 1.0 is formed using ink compositions with low color density. As a result, an improvement in light resistance of a light magenta ink composition can be linked to enhancing the light resistance of photographic images and prolonging the light resistance life of the ink set. In comparison with an ink composition having high color density, an ink composition having low color density does not require such strong chromogenicity, and other properties such as light resistance and the like become important.
As noted above, the ink compositions used in the inkjet printing method are mainly solutions wherein various dyes are dissolved in water, an organic solvent, or a liquid mixture thereof, and various surfactants and additives are added thereto for the purpose of improving the properties of the ink and increasing print quality and storage life of the printed matter. However, some of these surfactants and additives have high foamability despite their great effectiveness in improving ink composition properties, and an ink composition has been proposed wherein a specific defoaming agent and the like is combined therewith (see JP-A-2004-315739).